Colour brightness can be understood as the variation in how a colour is perceived by an observer under well-lit conditions compared to its more muted appearance when in shadow or under poor illumination.
Hue refers to the perceived difference between colours and is usually described using names such as red, yellow, green, or blue.
Saturation refers to the vividness of a colour compared to an unsaturated colour.
Brightness refers to the perceived difference in the appearance of colours under ideal sunlit conditions compared to poor lighting conditions where a hue’s vitality is lost.
Brightness can be measured as a percentage from 100% to 0%.
As the brightness of a fully saturated hue decreases, it appears progressively darker and achromatic.